PENETRATION OF IRON PLATES BY STEEL SHOT. 411 



which penetrated and liad some little force left in it, it is to be expected that 

 a force of 542 toiis should act as it did. It appears that a reduction of 

 2 0Z3. in the charge, and consequent diminution of " work" to 525 foot-tons 

 was sufficient to prevent complete penetration (round 1161), although it ap- 

 parently required but a small blow with a hammer to separate the piece of 

 plate at the back of the point struck : as this effect was produced by the shot 

 moving with the highest velocity, it is a convincing proof that with steel shot 

 the penetration is not proportional to a higher power than the square of the 

 velocity. 



2. Round 1164 is the only anomalous round in the present series : it was 

 supposed to be fired with exactly the same charge as round 1158 ; yet the 

 penetration was inferior, and the observed velocity less. It is difficult to 

 account for this except on the supposition that, throiigh some oversight, a 

 smaller charge was employed, or that the projectile was not quite rammed 

 home. 



3. It is clearly proved that plate 2 was of somewhat better quality 

 than plates 1 and 3. The fracture showed a better weld ; and this is evi- 

 dent by the increased resistance it offered to the projectiles — round 11G5 

 especially. 



It is difficult to guard against this cause of error, which is one of the 

 many that beset this question. 



From these experiments, the following practical conclusions may be drawn 

 when the 2yrojectiles arc fired direct. 



1. An unbacked wrought-iron plate will be perforated with equal facility 

 by solid steel shot of a similar form of head, and having the same diameter, 

 provided they have the same vis viva on impact ; and it is immaterial whether 

 this vis viva be the result of a heavy shot and low velocity, or a light shot 

 and a high velocity. 



2. An unbacked iron plate wiU be penetrated by solid steel shot of the 

 same form of head but different diameters, provided their striking vis viva 

 varies as the diameter nearly — that is as the circumference of the shot. 



3. That the resistance of unbacked wrought-iron plates, to absolute pene- 

 tration by solid steel shot of similar form and equal diameter, varies as the 

 square of their thickness nearly *, up to 5g inches. 



4. These experiments have proved that although, in the case of cmt iron, 

 a light projectile moving with a high velocity will indent iron plates to a 

 greater depth than a heavier projectile with a low velocity but equal " work," 

 it is not as necessary that there should be a high velocity when the projectiles 

 are of a hard material, such as steel and chilled iron ; and this result wUl be 

 much in favour of rifled guns, by enabling them to prove effective with com- 

 paratively moderate charges. 



If wo -wish to put these results in an algebraic form, wc shall have, taking 

 the units as the pound and the foot, 



^=2*Rt6^t, (1) 



* Tliis is only true wlien the plates arc of the best quality. It is well known that it is 

 easier to make a thin than a thick plate, and that the latter is liable to imperfect welding 

 in the process of rolling. The manufacture of armour-plates has, however, been so much 

 iniproved of late, that it is practically allowable to assume that theii- resistance varies as 

 the square of their thickness, witliin ordinary limits. 



t The above might be put as follows: foot-tons =^6"<?, where d i.s the diameter of the 

 projectile. The circumference, however, is preferred as better representing the portion of 

 iron actually sheared. *^ 



